Gas chromatography is an analytical technique which entails the separation and often identification of individual compounds, or groups of compounds, within a mixture. A gas chromatograph (GC) takes a small sample of liquid or gas that is introduced into a carrier stream of the same of another gas and identifies the amounts of various compounds within the sample, often in the form of a chromatograph. A chromatograph is a line chart with the horizontal axis identifying different compounds and the vertical axis providing an intensity related to the concentration. The carrier stream typically comprises helium, hydrogen, or nitrogen. The total amount of a compound in a given sample is generally related to the area under the peak associated with that particular compound. A highly sensitive detector can be utilized for the detection of these various compounds passing through a column of the GC. The commonly utilized detectors include, for example, flame ionization detector (FID), nitrogen-phosphorous detector (NPD), electron capture detector, and mass spectrometer. Such conventional detectors, however, are cumbersome or expensive to use, others generate electrons and ions by means of radioactive elements which can be hazardous and not suitable for general applications.
Micro discharge device (MDD) detector can be utilized for detecting the presence of molecules in a gas sample on the basis of their optical emission spectrum as excited and emitted by that discharge. The majority of prior art MDD detectors are designed with a minimum discharge region, which possess a minimal overlap with the analyte's flow path. The problem associated with such detectors is an unacceptable large dead-volume before emission region which makes the device less useful for high efficiency chromatography. Also, many devices have no barrier between the discharge and the electrodes making the devices less durable. Also, such detectors possess moderate to low intensity emissions in helium or other inert noble carrier gases and little to no emissions in an air carrier gas at low voltages.
FIG. 1 illustrates an electric field distribution of a prior art micro discharge device 100. The gas flow direction is indicated by arrow 125. As depicted in FIG. 1, the highest electric field region is not in the flow channel. The electric field ratio of the micro discharge device 100 at the middle of the channel as indicated by arrow 120, is equivalent to 3.8. Hence, the MDD 100 requires very high operating voltage to create high electric field strengths in the flow path. The large fields often cause durability issues. Without the very large field, a lower intensity discharge signal results for MDD 100.
Based on the foregoing, it is believed that a need exists for an improved micro discharge device capable of low voltage discharges in a variety of carrier gases for detection and/or ionization as disclosed in greater detail herein.